With the popularization of portable instruments in recent years, various batteries and capacitor devices such as electric double-layer capacitor are becoming lightweight and also, the production thereof is abruptly increasing. Furthermore, in view of the popularization in the future of hybrid car, electric car and the like, which are highly expected from an environmental aspect, there is a demand for capacitor devices to have larger size and higher performance. Among the batteries, nonaqueous batteries, such as Li primary battery and Li ion secondary battery are growing because of their high voltage and high energy density. Also, electric double-layer capacitors using an active carbon electrode having a high specific surface area as the polarizable electrode are also growing because of their high power density.
With respect to the display material, flatness and small thickness are being taken notice of and studies on improvements of liquid crystal, organic electroluminescent device and electrochromic (ECD) devices are aggressively proceeding. Among these, an ECD device exhibits color change by an electrochemical reaction, does not spontaneously emit light and is low in response speed. However, because of its memory property, the ECD device is attracting attention in view of its original purpose such as light-shielding glass, rather than as a display device.
These capacitor devices and ECD devices each uses an electrochemical reaction and the electrolyte material used therein is demanded to have higher performance. The properties required for the electrolyte material include high ionic conductivity, broad range of electrochemical stability, impregnation property into various electrodes, heat resistance, environmental resistance and safety. In particular, a Li (ion) battery, and a nonaqueous electric double-layer capacitor as a nonaqueous capacitor device are attracting attention at present because of their high voltage and high energy density. The electrolyte material used therefor is particularly demanded to satisfy the following requirements: to be improved in the ionic conductivity, to have an electrochemical stability range broad enough to endure high voltage use, to be easily compounded with various electrode materials and to have excellent safety.
Conventional liquid electrolytes have a problem in that the safety and reliability decrease due to liquid leakage or volatilization. In order to solve this problem, a solid polymer electrolyte obtained by solidifying an electrolyte salt with a polymer or the like is being taken notice of in recent years. Examples thereof include a solid polymer electrolyte characterized by the introduction of a polyether chain into a polymer (see, JP-A-4-211412 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)). This solid polymer electrolyte is improved in safety and stability, but suffers from reduction in ionic conductivity or deterioration in the compounding property with various electrode materials and from a problem that when the solid polymer electrolyte is used in various electrochemical devices, the device has small takeout current.
In order to solve these problems of the solid polymer electrolyte, the present inventors have proposed a solid polymer electrolyte using a polymer having a carbonate structure, and a polymerizable compound and a polymerizable composition for obtaining the solid polymer electrolyte (see, for example, JP-A-11-149823 and JP-A-11-149824).
JP-A-1-311573 describes an electrochemical apparatus using a solid polymer electrolyte comprising a polymer having bonded thereto a side chain having no active hydrogen atom, where poly(ethylene ether carbonate) end capped with methacrylate is an example of the polymer.
JP-A-9-147912 describes a solid polymer electrolyte having both flexibility and rigidity, and improved in adhesive property to alkali electrode and in interface resistance by using a copolymer of poly(alkylene(ether)carbonate end capped with methacrylate, similar to JP-A-1-311573, and a polyether end capped with methacrylate.
Also, JP-A-62-30147 and JP-A-62-30148 disclose a solid polymer electrolyte using polyalkylene carbonate having a specific structure, which enhances the compatibility of an organic solvent or an electrolyte salt and improves the mechanical properties.
The carbonate structure has a high dielectric constant and therefore, improves the solubility of electrolyte salt and compatibility with various organic solvents and in turn, the solid polymer electrolyte is improved in ionic conductivity. Furthermore, a broad electrochemical stability range is ensured, which is suited for the fabrication of devices having a high voltage. However, a polymer having a carbonate structure has a high viscosity compared with polyether-based polymers conventionally used for the polymer solid electrolyte and suffers from poor compounding property with various electrode materials.